INTERNATIONAL STANDARD ISO 16639 First edition 2017-01 Surveillance of the activity concentrations of airborne radioactive substances in the workplace of nuclear facilities Surveillance de l’activité volumique des substances radioactives dans l’air des lieux de travail des installations nucléaires Reference number ISO 16639:2017(E) © ISO 2017 ISO 16639:2017(E) COPYRIGHT PROTECTED DOCUMENT © ISO 2017, Published in Switzerland All rights reserved Unless otherwise specified, no part o f this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission Permission can be requested from either ISO at the address below or ISO’s member body in the country o f the requester ISO copyright o ffice Ch de Blandonnet • CP 401 CH-1214 Vernier, Geneva, Switzerland Tel +41 22 749 01 11 Fax +41 22 749 09 47 copyright@iso.org www.iso.org ii © ISO 2017 – All rights reserved ISO 16639:2017(E) Page Contents Foreword v Introduction vi Scope Normative references Terms and definitions Symbols Developing the surveillance program 5.1 5.2 5.3 5.4 Location of samplers and monitors 6.7 General Types o f air flow studies 6.2.1 General 6.2.2 Qualitative airflow studies 6.2.3 Quantitative airflow studies 10 Location of samplers for estimating committed effective dose 10 Location of samplers for evaluating effectiveness of containment 11 Location of samplers for posting of air contamination areas 11 Location of portable samplers 12 Location o f CAM for continuous monitoring o f the activity concentration 12 7.1 7.2 7.3 General 12 Sampling of aerosol particles 12 Gas Sampling 13 8.1 8.2 8.3 8.4 Determining the average activity concentration 14 Uncertainty 14 Techniques for correcting for radon progeny interference 15 Evaluating changes in activity concentration over time 15 6.1 6.2 6.3 6.4 6.5 6.6 Collection of samples 12 Evaluation of sampling results 14 8.5 Review of sampling results 15 Evaluating the effectiveness of the sampling program 16 9.1 9.2 10 Reasons for conducting a surveillance programme 5.1.1 General 5.1.2 Sampling when respiratory protective equipment is used 5.1.3 Sampling to establish air contamination areas 5.1.4 Air sampling as a basis for determining worker intakes 5.1.5 Air monitoring for early warning o f elevated air concentrations Graded approach to sampling Frequency o f sampling 5.3.1 General 5.3.2 Grab vs continuous sampling 5.3.3 Continuous monitoring o f activity concentrations 5.3.4 Prompt analysis o f certain samples Substitutes for air sampling General 16 Dose-based assessment o f the adequacy o f the sampling program 16 Quality assurance and quality control 17 10.1 General 17 10.2 Sample identification, handling, and storage 17 10.3 Sampling and monitoring equipment 17 10.3.1 General 17 10.3.2 Performance of measuring instruments 18 © ISO 2017 – All rights reserved iii ISO 16639:2017(E) 10.3.3 Air in-leakage testing 18 10.4 Documentation and record keeping 18 Annex A (informative) Examples for the determination of uncertainty, decision threshold and detection limit according to ISO 11929 20 (informative) Correcting for the interference of radon progeny 27 Annex C (informative) Normalized concentration and exposure 29 Annex D (informative) Example applications of evaluating sampling program sensitivity Annex B from the viewpoint of potential missed exposure 30 Bibliography 32 iv © ISO 2017 – All rights reserved ISO 16639:2017(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work o f preparing International Standards is normally carried out through ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters o f electrotechnical standardization The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part In particular the different approval criteria needed for the di fferent types o f ISO documents should be noted This document was dra fted in accordance with the editorial rules of the ISO/IEC Directives, Part (see www.iso org/directives) Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f patent rights ISO shall not be held responsible for identi fying any or all such patent rights Details o f any patent rights identified during the development o f the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso org/patents) Any trade name used in this document is in formation given for the convenience o f users and does not constitute an endorsement For an explanation on the meaning o f ISO specific terms and expressions related to formity assessment, as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www.iso org/iso/foreword.html The committee responsible for this document is ISO/TC 85, Nuclear energy, nuclear technologies, and radiological protection , Subcommittee SC 2, Radiological protection © ISO 2017 – All rights reserved v ISO 16639:2017(E) Introduction Sampling o f airborne radionuclides and monitoring o f activity concentration in workplaces are critically important for maintaining worker sa fety at facilities where dispersible radioactive substances are used Specifically, air sampling and monitoring are critical for evaluation o f containment integrity, evaluation of effectiveness of contamination control programs and work practices, providing measurements for qualitative dose assessment, providing a general assessment of the level of the airborne hazard in a room, and for providing workers an immediate warning when the activity concentration exceeds sa fe levels This document sets forth guidelines and performance criteria for sampling airborne radioactive substances and monitoring activity concentration in the workplace o f nuclear facilities Emphasis is on health protection for workers in indoor environments This document provides best practices and per formance-based criteria for the use o f sampling devices and systems, including delayed radioactivity measurement samplers and continuous air monitors Specifically, this document covers air sampling program objectives, design o f sampling and monitoring programs to meet program objectives, methods for air sampling and monitoring in the workplace, and quality assurance to ensure system per formance toward protecting workers against unnecessary inhalation exposures Taken together, these activities constitute the sampling or surveillance program The primary purpose o f the surveillance o f airborne activity concentrations in the workplace is to evaluate and mitigate inhalation hazards to workers in facilities where these may become airborne Results o ften provide the basis for development and evaluation o f control procedures and may indicate i f engineering controls or operational changes are necessary The surveillance can consist o f two general techniques The first is retrospective sampling, in which constituents of the air are sampled, the collection medium is removed and taken to a radiation detector system and analysed for radioactive substances, and the activity concentration results made available at a later time In this context, the measured activity concentrations are evaluated retrospectively The second approach is real-time monitoring, in which activity concentrations are continuously monitored so that workers can be warned that a significant release o f airborne activity may have occurred In implementing an effective sampling program, it is important to achieve a proper balance between the two general approaches o f the program The specific balance depends on the hazard level o f the work and the characteristics o f each facility When designing a surveillance program, the optimization of worker protection minimizes internal considerations that are associated with the use of the radioactive substance and external exposures while balancing social, technical, economic, practical, and public policy A comprehensive surveillance program should also consider that the monitoring program is only one element of a comprehensive radiation protection program Therefore, individuals involved with the monitoring program should interact with personnel working in the other elements of the radiation protection program, such as contamination control and internal dosimetry vi © ISO 2017 – All rights reserved INTERNATIONAL STANDARD ISO 16639:2017(E) Surveillance of the activity concentrations of airborne radioactive substances in the workplace of nuclear facilities Scope This document provides guidelines and performance criteria for sampling airborne radioactive substances in the workplace Emphasis is on health protection of workers in the indoor environment This document provides best practices and performance-based criteria for the use of air sampling devices and systems, including retrospective samplers and continuous air monitors Specifically, this document covers air sampling program objectives, design o f air sampling and monitoring programs to meet program objectives, methods for air sampling and monitoring in the workplace, and quality assurance to ensure system per formance toward protecting workers against unnecessary inhalation exposures The primary purpose o f the surveillance o f airborne activity concentrations in the workplace is to evaluate and mitigate inhalation hazards to workers in facilities where these can become airborne A comprehensive surveillance program can be used to — determine the e ffectiveness o f administrative and engineering controls for confinement, — measure activity concentrations o f radioactive substances, — alert workers to high activity concentrations in the air, — aid in estimating worker intakes when bioassay methods are unavailable, — determine signage or posting requirements for radiation protection, and — determine appropriate protective equipment and measures Air sampling techniques consist o f two general approaches The first approach is retrospective sampling, in which the air is sampled, the collection medium is removed and taken to a radiation detector system and analysed for radioactive substance, and the concentration results made available at a later time In this context, the measured air concentrations are evaluated retrospectively The second approach is continuous real-time air monitoring so that workers can be warned that a significant release o f airborne radioactivity may have just occurred In implementing an e ffective air sampling program, it is important to achieve a balance between the two general approaches The specific balance depends on hazard level o f the work and the characteristics o f each facility A special component o f the second approach which can apply, i f properly implemented, is the preparation of continuous air monitoring instrumentation and protocols This enables radiation protection monitoring o f personnel that have been trained and fitted with personal protective equipment (PPE) that permit pre-planned, defined, extended stay time in elevated concentrations o f airborne radioactive substances Such approaches can occur either as part o f a planned re-entry o f a contaminated area following an accidental loss o f containment for accident assessment and recovery, or part o f a project which involves systematic or routine access to radioactive substances (e.g preparing process material containing easily aerosolized components), or handling objects such as poorly characterized waste materials that may contain radioactive contaminants that could be aerosolized when handled during repackaging In this special case, the role of continuous air monitoring is to provide an alert to health physics personnel that the air concentrations o f concern have exceeded a threshold such that the planned level o f protection a fforded by PPE has been or could be exceeded This level would typically be many 10’s or 100’s o f times higher than the derived air concentration (DAC) established for unprotected workers The monitoring alarm or alert would therefore be designed not to be confused with the normal © ISO 2017 – All rights reserved ISO 16639:2017(E) monitoring alarm, and the action taken in response would be similarly targeted at the specific site and personnel involved The air sampling strategy should be designed to minimize internal exposures and balanced with social, technical, economic, practical, and public policy considerations that are associated with the use o f the radioactive substance A comprehensive air sampling strategy should also consider that the air sampling program is only one element of a broader radiation protection program Therefore, individuals involved with the air sampling program should interact with personnel working in other elements of the radiation protection program, such as contamination control and internal dosimetry This document does not address outdoor air sampling, e ffluent monitoring, or radon measurements Normative references The following documents are re ferred to in the text in such a way that some or all o f their content constitutes requirements o f this document For dated re ferences, only the edition cited applies For undated re ferences, the latest edition o f the re ferenced document (including any amendments) applies ISO 11929, Determination of the characteristic limits (decision threshold, detection limit and limits of the confidence interval) for measurements o f ionizing radiation — Fundamentals and application Terms and definitions For the purposes o f this document, the following terms and definitions apply ISO and IEC maintain terminological databases for use in standardization at the following addresses: — IEC Electropedia: available at http://www.electropedia org/ — ISO Online browsing platform: available at http://www.iso org/obp 3.1 accuracy closeness of agreement between a measured value and a true value 3.2 aerodynamic diameter Da diameter o f a sphere with density 000 kg·m-3 that has the same sedimentation velocity in quiescent air as the actual particle o f arbitrary shape and density 3.3 aerosol dispersion of solid or liquid particles in air or other gas Note to entry: An aerosol is not only the aerosol particles 3.4 airborne radioactive substance radioactive substance dispersed in the air in the form of dusts, fumes, particulates, mists, vapours, or gases 3.5 air contamination area area accessible to individuals where the measured activity concentrations o f an airborne radioactive substance exceeds or is likely to exceed the applicable national criteria © ISO 2017 – All rights reserved ISO 16639:2017(E) 3.6 air sampler device designed to pass a known volume o f air containing a radioactive substance through a filter or other media and thereby trapping the airborne radioactive substance on the sampling media 3.7 annual limit on intake ALI derived limit for the amount o f radioactive substance (in Bq) taken into the body o f an adult worker by inhalation or ingestion in a year 3.8 breathing zone BZ uni form description o f the volume o f air directly around the worker‘s upper body and head, which may be drawn into the lungs during the course of breathing Note to entry: An air sample representative o f the breathing zone is usually considered to be representative i f drawn from within about 30 cm of the worker’s head 3.9 breathing zone sampler BZA air sampler located in the breathing zone Note to entry: Other common terms include “personal air sampler” (PAS), “personal air monitor” (PAM), “lapel air samplers” or “fixed air sampler” Note to entry: In the case o f workers using PPE which includes full face (or even whole body suit) respirator equipment and supplied air, as when preparing for entry into high levels o f airborne radioactive substances, special BZA or protective equipment samplers may be needed Such BZAs are not always mandated then, but the decision should be based on the contaminant levels and types o f PPE involved and the potential for contamination entering the suit or air immediately surrounding the suit just as PPE are being ffed 3.10 continuous air monitor CAM instrument that continuously monitors the airborne activity concentration on a near real-time basis 3.11 continuous monitoring active and continual monitoring o f activity concentration in room air in near real time Note to entry: This approach uses continuous air monitors to assess activity concentration in air and can alarm when predetermined levels are exceeded 3.12 derived air concentration DAC concentration o f a radionuclide in air that, i f breathed over the period o f a work year, would result in the intake of one ALI for that radionuclide Note to entry: The DAC is calculated by dividing the ALI by the volume o f air breathed by re ference man under light-activity work during a working year (in Bq·m-3 ) Note to entry: The parameter values recommended by the International Commission on Radiological Protection for calculating the DAC are a breathing rate of 1,2 m3 ·h-1 and a working year o f 000 h (i.e 400 m3 ) Note to entry: The air concentration can be expressed in terms o f a number o f DAC For example, i f the DAC for a given radionuclide in a particular form is 0,2 Bq·m -3 and the observed concentration is 1,0 Bq·m -3 , then the observed concentration can also be expressed as DAC (i.e 1,0 divided by 0,2) © ISO 2017 – All rights reserved ISO 16639:2017(E) Note to entry: The derived air concentration-hour (DAC-h) is an integrated exposure and is the product o f the concentration of a radioactive substance in air (expressed as a fraction or multiple of DAC for each radionuclide) and the time of exposure to that radionuclide, in hours [SOURCE: References [5] and [10], modified] 3.13 detection limit LD smallest true value o f the measurand which ensures a specified probability o f being detectable by the measurement procedure Note to entry: For a given type-I error (or false alarm probability, i.e typically 0,05), L D is the lowest net count (or rate) with the desired probability o f detection, i.e typically 0,95 (otherwise stated as a type-II error o f 0,05 or a missed detection probability o f %) Note to entry: The measurand is the quantity subject to measurement 3.14 grab sample air sample o f a su fficient volume drawn over a relatively short duration 3.15 intake activity o f a radionuclide taken into the body in a given time period or as a result o f a given event [SOURCE: ISO 20553:2006, 3.10] 3.16 personal air monitor personal air sampler breathing zone sampler 3.17 personal protective equipment PPE equipment designed to limit worker exposure to contaminants in the air or that are easily resuspended from contaminated surfaces Note to entry: Includes partial or full- face respirators, face masks, gloves, boots, whole body anti-contamination coveralls, and self-contained breathing apparatus (SCBA), depending on conditions 3.18 potential missed exposure PME time-integrated activity concentration or maximum activity concentration, as applicable, that can acceptably be missed Note to entry: The detection limit o f the method o f measuring the activity concentration shall be less than or equal to the selected PME, which is defined according to ALARA/ALARP principles, and below legal limits 3.19 sampling collection o f a radioactive substance on media such as filters, absorbers or adsorbers that is analysed for radioactive content after collection 3.20 standard reference conditions conditions of temperature and pressure to which measurements are referred for standardization Note to entry: For this document, the standard re ference conditions are 25 °C temperature and 101 325 Pa pressure © ISO 2017 – All rights reserved ISO 16639:2017(E) Annex A (informative) Examples for the determination of uncertainty, decision threshold and detection limit according to ISO 11929 A.1 General This annex demonstrates the application of ISO 11929 to a direct measurement of an airborne rad ionucl ide a nd s ampl i ng o f rad io ac tive aero s ol p a r ticle s on a fi lter with on l i ne or delaye d cou nti ng T he fi rs t s tep i n de term i n i ng uncer ta i nty, de c i s ion th re shold and de te c tion l i m it accord i ng to I S O 119 i s the s truc tion o f an ana lytic a l mo del o f the me as u rand given in Formula (A.1): Y as a function G of its input quantities Xi, as (A.1) Y = G( X1 , , X m ) u( y f y in dependence on the estimates xi of the input quantities Xi and their respective uncertainties u(xi) can be calculated according to Formula (A.2): T he u ncer tai nty u ) o m ∂G = i = ∂X i ( y) ∑ a pri mar y me as u rement re s u lt u xi ( ) (A.2) X1 i s a s s igne d a s p e ci a l p ar t i n the c a lc u lation o f the de ci s ion th re s hold and de te c tion l i m it To fu l fi l th i s part, X1 has to meet additional requirements — X1 x1 , is not given when a true value, ỹ, of the measurand, Y, is i s ta ken a s that quantity who s e va lue, s p e ci fie d, and — u(x1) is given as a function h1 (x1) of x1 ũ( ỹ ) of the true value ỹ u (x1 ) is given as a function h1 (x1) of x1 In such cases, y f ỹ and Formula (A.1), formulated for the estimates xi of the input quantities Xi shall be solved for x1 ỹ, the value x1 can be calculated, which results in x1 as a function of ỹ and x2 ,…, xm This function shall replace x1 in Formula (A.2) and in u (x1) = h (x1 ũ( ỹ ) instead of u ( y) The decision threshold, y* α quantile of the standardized normal distribution k α as, given in Formula (A.3): y * = k1 − α u ( ) (A.3) I n mo s t c as e s , the u ncer tai nty c a n b e expl icitly s p e c i fie d , provide d that s l l b e orma l ly replace d b y With a s p e ci fie d ) , wh ich fi na l ly yield s , i s c a lc u late d u s i ng the 1− 1− The detection limit, y# f standardized normal distribution k β, as given in Formula (A.4): , c an b e derive d rom the de ci s ion th re s hold uti l i z i ng the 1− β quantile of the 1− ( ) y # = y * + k1 − β u y # (A.4) Formula (A.4) is then solved for the unknown detection limit, y# 20 © ISO 2017 – All rights reserved ISO 16639:2017(E) A.2 Direct measurement of airborne activity A.2.1 Model T he a i r u nder s ideration i s me a s u re d d i re c tly with a de te c tor pl ace d i n a defi ne d volu me q through a sampling line and reaches the measuring volume V after a time t1 C f λ in V counting n g pulses in the counting time t2 f f η and background count rate r0 The differential equation for the number of atoms N of the radionuclide in the measuring volume can f f C0 at the sampling point, as given in Formula (A.5): T he r i s s ample d with a flow rate T he ac tivity concentration o the rad ionucl ide with de c ay s tant with a de te c tor o thu s b e ormu l ate d i n dep endence o ( ) = C0 e − λ t ∂N t ∂t q λ i s me a s ure d b y e fic ienc y the rad ionucl ide ac tivity concentration () −λN t − N (t ) q (A.5) V where the fi rs t term on the right s ide de s c rib e s the i ncom i ng a i r, the s e cond term the rad io ac tive de c ay in the measuring volume and the right term the removal of air from the measuring volume The solution of the differential equation is, as given in Formula (A.6): −(λ V + q)t V C0 q − λ t1 V 1−e N( t ) = e (A.6) ( λ λV +q ) T he me as u ri ng s igna l i s ob ta i ne d by cou nti ng the de cayi ng atom s i n the ti me i nter va l given in Formula (A.7): ng = t2 ( λ V + q ) C0 q η V λ V + q t − V − e V dt = λt e λV +q ( t2 ∫ (η λ N ( t ) + r0 ) ) ( ) Thus, C0 can be determined as, as given in Formula (A.8): C0 = e (λ V + q ) (n g − r t ) λ t1 ( function of its input quantities: u (C0 ) ∂C0 + ∂V ∂C u2 n g + ∂t + r0 t (A.7) u ( ) ∂C (V ) + ∂q © ISO 2017 – All rights reserved (A.8) ) T he u ncer tai nty i s c a lc u late d i n the ∂C = ∂n g yield i ng , as t2 ( λ V + q ) V q η V λ V + q t2 − V − e A.2.2 Determination of uncertainty t2 fol lowi ng Formula (A.9) ∂C u (t1 ) + ∂t u ∂C (q) + ∂r0 2 , gi vi ng the uncer ta i nty ∂C u ( t ) + ∂λ u (r ) 2 ∂C u (λ ) + ∂η ( ) of C0 as u C0 u (η ) (A.9) 21 ISO 16639:2017(E) A.2.3 Determination of decision threshold and detection limit The number of gross counts n g f value of C0 x1 Assuming a Poisson distribution of the counts, the f h (n g f n g The functional relation of n g with C0 is Formula (A.7), enabling the calculation of decision threshold and detection limit according to Formulae (A.3) and (A.4) i s the on ly i nput qua ntity i n the mo del wh ich i s u n known or a given and i s accord i ngly de s ignate d a s uncer tai nty unc tion ) i s given by the s quare ro o t o a l re ady defi ne d i n A.2.4 Numerical example Table A.1 gives numerical values for the calculations according to Formulae (A.3) to (A.9) Table A.1 — Numerical values for input parameters and resulting uncertainty, decision threshold and detection limit Quantity Value ng 190 600 2,2E-3 6,3E-2 2,6E-4 7,8E-3 1,1E-4 80 C0 234 t1 t2 q V η r0 λ decision thresholdb * C detection limitb # C a b , Estimated uncertaintya Unit 60 0,1 2E-4 1E-3 2E-5 4E-4 1E-6 s s m3 m3 s s s · s −1 −1 −1 −1 174 B q· m −3 392 , · B q −1 B q· m −3 099 B q· m −3 Standard deviation of a normal distribution I f the p ro b ab i l i ty e qu a l to % then k1− I f the p ro b ab i l i t y 1− α o f the er ro r o f the fi rs t ki nd a nd the p ro b ab i l i ty β of the error of the second kind are both considered α , k β = 1,645 1− γ fo r the co n fidence i nter va l i s co n s idere d e qu a l to ,9 the n γ = 0,05 and k 1− γ/2 = 1,96 A.3 Measuring activity on a filter during sampling A.3.1 Model T h i s e xample s iders the me a s u rement o f ac tivity on a fi lter wh i le it i s b ei ng col le c te d on that fi lter T he a i r i s s a mple d with a flow rate q th rough a s a mpl i ng l i ne a nd re ache s the fi lter a fter a ti me t1 The λ i s me a s u re d b y cou nti ng n g pulses of the ac tivity dep o s ite d on the fi lter i n the counti ng ti me t2 with a de te c tor o f e fficienc y η and background ac tivity concentration C o f the rad ionucl ide with de c ay s ta nt count rate r0 22 © ISO 2017 – All rights reserved ISO 16639:2017(E) The differential equation for the number of atoms N of the radionuclide on the filter can thus be ormulated in dependence o f the radionuclide activity concentration C0 at the sampling point, as given in Formula (A.10): f ( ) = C0 e − λ t ∂N t ∂t q λ () (A.10) −λN t where the first term on the right side describes the deposition on the filter and the second term the radioactive decay o f the activity on the filter Assuming N0 atoms o f the radionuclide already on the filter at the start o f sampling, the solution o f the di fferential equation is, as given in Formula (A.11): C q e − λ t1 −λ t −λ t N( t ) = 1−e + N0 e λ2 (A.11) The measuring signal is obtained by counting the decaying atoms in the time interval t2 yielding, as given in Formula (A.12): ng = t2 ∫ (η λ N ( t ) + r ) 0 − λ t1 η C0 e −λ t dt = η N0 − e + λ2 Thus, C0 can be determined as given in Formula (A.13) q λ t2 + e − λ t2 − + r0 t − λ t2 n g − η N0 − e − r0 t C0 = t λ − q η λ t + e − A.3.2 Determination of uncertainty λ2 e λ t1 The uncertainty is calculated in the following function of its input quantities: u (C0 ) (A.12) ∂C = ∂n g ∂C0 + ∂N0 ∂C u2 n g + ∂t u ( ) ∂C ( N0 ) + ∂q (A.13) Formula (A.14) , giving the uncertainty u(C0) of C0 as ∂C u ( t ) + ∂t 2 u ∂C (q) + ∂r0 2 ∂C u ( t ) + ∂λ ∂C u ( λ ) + ∂η u (r ) 2 u (η ) (A.14) A.3.3 Determination of decision threshold and detection limit The number of gross counts n g is the only input quantity in the model which is unknown for a given value of C0 and is accordingly designated as x1 Assuming a Poisson distribution of the counts, the uncertainty function h (n g) is given by the square root o f n g The functional relation of n g with C0 is already defined in Formula (A.12), enabling the calculation of decision threshold and detection limit according to Formulae (A.3) and (A.4) A.3.4 Numerical example Table A.2 gives numerical values for the calculations according to Formulae (A.3), (A.4), (A.13) and (A.14) © ISO 2017 – All rights reserved 23 ISO 16639:2017(E) Table A.2 — Numerical values for input parameters and resulting uncertainty, decision threshold and detection limit Quantity ng 100 600 3,3E-4 1,3E-2 0,05 1,0E-6 30 C0 t1 t2 q N0 η r0 λ decision thresholdb * C , 10 0,1 3E-5 5E4 1E-3 1E-3 1E-9 s s m3 s -1 -1 s -1 s -1 ·Bq B q· m −3 B q· m −3 28 # · s −1 B q· m −3 Standard deviation of a normal distribution a b I f the p ro b ab i l i ty e qu a l to % then M e a s u r α o f the er ro r o f the fi rs t ki nd a nd the p ro b ab i l i ty β of the error of the second kind are both considered k1− α, k1− β I f the p ro b ab i l i t y 1− A Unit 12 detection limitb , C Estimated uncertaintya Value i = 1,645 γ fo r the co n fidence i nter va l i s co n s idere d e qu a l to ,9 the n γ = 0,05 and k n g a c t i v i t y o n a f i l t e r a f t e r s a m p l i n 1− γ/2 = 1,96 g A.4.1 Model T h i s exa mple s iders the me a s u rement o f ac tivity on a fi lter a fter it s b e en remove d from the s a mpl i ng s ys tem T he air i s s ampled with a flow rate ac tivity concentration C of q through a s ampli ng line and reaches the fi lter a fter a ti me the radionuclide with decay cons tant the time interval t2 counting ng pulses in the time interval t4 λ t1 , then the fi lter i s removed T he ac tivity on the fi lter is meas ured a fter a delay 24 − The is s ampled at the fi lter lo cation i n t3 with a detec tor o f e fficienc y η t3 by and background count rate r0 © ISO 2017 – All rights reserved ISO 16639:2017(E) The differential equation for the number of atoms N of the radionuclide on the filter during sampling is identical to Formula (A.10) and can be formulated in dependence of the radionuclide activity concentration C0 at the sampling point, as given in Formula (A.15): ( ) = C0 e − λ t ∂N t ∂t λ q () (A.15) −λN t where the first term on the right side describes the deposition on the filter and the second term the radioactive decay o f the activity on the filter Assuming an activity free filter at the start o f sampling, the solution of the differential equation is, as given in Formula (A.16): C0 q e N( t ) = − λ t1 λ2 −λ t 1−e (A.16) At the end of sampling, N(t2 ) atoms of the radionuclide are present on the filter The activity decreases herea fter by radioactive decay As a new di fferential equation governs the process, a di fferent clock is started at t2 The measuring signal is obtained by counting the decaying atoms in the time interval [t3 , t4] yielding, as given in Formula (A.17): t4 ∫ (η λ N ( t ) + r0 ) ng = t3 = − λ t1 η C0 q e λ2 t4 − λ t1 C qe dt = η λ λ2 t3 ∫ − λ t2 1−e − λ t − λ t3 − λ t4 −e 1−e e + r0 t − t Thus, C0 can be determined as, as given in Formula (A.18): λ2 e C0 = λ t1 −λ t + r0 dt e (n g − r (t − t3 ( (A.17) ) )) (A.18) −λ t −λ t −λ t q η − e e − e A.4.2 Determination of uncertainty The uncertainty is calculated in the following function of its input quantities: u (C ) ∂C = ∂n g ∂C u ng + ∂t ( ) Formula (A.19) , giving the uncertainty u(C0) of C0 as ∂C u ( t ) + ∂t 2 u ( t ) ∂C + ∂t ∂C u ( t ) + ∂t ∂C u λ + ∂C u η + ∂C u q + ∂C u r + ( ) ( ) q ( ) ∂r ( ) ∂λ ∂η ∂ 2 2 2 2 u ( t ) (A.19) A.4.3 Determination of decision threshold and detection limit The number of gross counts n g is the only input quantity in the model which is unknown for a given value of C0 and is accordingly designated as x1 Assuming a Poisson distribution of the counts, the uncertainty function h (n g) is given by the square root o f n g The functional relation of n g with C0 is already defined in Formula (A.17), enabling the calculation of decision threshold and detection limit according to Formulae (A.3) and (A.4) A.4.4 Numerical example Table A.3 gives numerical values for the calculations according to Formulae (A.3), (A.4), (A.18) and (A.19) © ISO 2017 – All rights reserved 25 ISO 16639:2017(E) Table A.3 — Numerical values for input parameters and resulting uncertainty, decision threshold and detection limit Quantity Value ng 10 604 800 17 526 24 726 3,3E-4 1,8E-2 7,8E-3 1,4E-7 223 C0 87 t1 t2 t3 t4 q η r0 λ decision thresholdb * C detection limitb # C a b Unit 0,5 20 20 3E-5 1E-3 5E-4 1E-10 47 s s s s m3 s -1 s s · B q −1 −1 −1 m B q· m −3 0,6 , · s −1 m B q· m −3 1,2 m B q· m −3 Standard deviation of a normal distribution I f the p ro b ab i l i ty e qu a l to % then α o f the er ro r o f the fi rs t ki nd a nd the p ro b ab i l i ty β of the error of the second kind are both considered , k1− α k1− β I f the p ro b ab i l i t y 1− 26 , Estimated uncertaintya = 1,645 γ fo r the co n fidence i nter va l i s co n s idere d e qu a l to ,9 the n γ = 0,05 and k 1− γ/2 = 1,96 © ISO 2017 – All rights reserved ISO 16639:2017(E) Annex B (informative) Correcting for the interference of radon progeny B.1 General Most radon progeny, being gamma emitters, can inter fere with the counting o f gamma emitters in air samples and continuous air monitoring instruments In the case o f particulate filter air sampling, the build-up o f short-lived radon progeny towards transient equilibrium presents a particular challenge A number o f sample analysis techniques are available for gross determination o f beta-gamma emitters collected during air monitoring These include ion chamber, liquid scintillator counting, beta scintillator (plastic scintillator), solid state (thick depletion ion-implant silicon for beta detection), and various gamma scintillator detector types for gamma spectroscopy [NaI(Tl), CsI(Tl), and other variants], HPGe (cooled) and similar high-resolution diode detectors, and some less commonly used solid state scintillator detectors Many strategies for handling samples be fore counting applicable for gross-alpha measurements are also relevant for gross-beta and gross-gamma counting However, spectroscopic techniques allow for much more targeted detection and counting and hence more effective elimination or correction for radon progeny inter ference B.2 Filter sampling The radon progeny inter ference builds up to equilibrium activities on the filter media in about four hours for the 222 Rn progeny and in about four days for the 220 Rn progeny For the most accurate gross analysis o f long-lived activity on the filter media post-sampling, it also requires about a four-hour wait for the decay o f the 222 Rn progeny and about a four-day wait for the decay o f the 220 Rn progeny prior to counting It should be noted that i f sampling times are quite short with respect to the time frame o f a day, then negligible quantities of 220 Rn progeny are present from typical environmental air concentrations and only the four-hour wait should be su fficient I f one is in need o f “early” results, then several “prompt” techniques are possible A spectroscopybased technique involves the use o f filter media that predominately collects the radon progeny on the filter sur face providing reasonably good resolution in the alpha-energy spectrum A fter a wait o f about 10 for the decay o f 218 Po, which peak is seen at 6,0 MeV, measurement by alpha spectrometry is performed to discriminate against the alpha radiation of 214Po, which peak is seen at 7,7 MeV 214Po is fed from the remaining beta-emitting radionuclides 214Pb and 214Bi For relatively accurate gross alpha results within a 24-hour period, it is recommended to use a two count method, one after the 222 Rn progeny have decayed to negligible levels (>4 h) and another about 18 h later to allow correction for the contribution of the longer lived 220 Rn progeny 212 Pb (10,64 hour half-life) The 212 Pb is in secular equilibrium with its alpha emitting daughters 212 Bi and 212 Po Formula (B.1) is used for this method © ISO 2017 – All rights reserved 27 ISO 16639:2017(E) Ac = where A2 − A1 e ( ) − λ ∆t (B.1) ( ) 1−e − λ ∆t c is the corrected gross alpha activity, in Bq; A1 is the gross alpha activity at time t1 , in Bq; A is the gross alpha activity at time t2 , in Bq; λ is the radioactive transition constant for 212 Pb, in s -1 ; A Δt is the time difference t2 − t1 B.3 Continuous air monitoring The correction for 222 Rn and 220 Rn progeny during continuous air monitoring is necessary to achieve adequate sensitivity for some radionuclides In particular, for longer-lived alpha-emitting transuranics, such as 238Pu, 239Pu, 240 Pu and 241 Am, the effective dose per unit intake by inhalation is very large For both kinds o f radon progeny, the alpha particles are emitted with energies higher than the energies o f the alpha particles emitted by the transuranics or for U and Th Most commercial CAMs are capable o f alpha spectrometry using silicon detectors Such detectors provide enough spectroscopic in formation to permit excellent background compensation for alpha emitters by predicting the background contributions in the energy regions o f interest (ROIs) o f U, Th, and the transuranics The 222 Rn progeny that contribute to background are 218 Po and 214Po, while the 220 Rn progeny that contribute to background are 212 Bi and 212 Po Using the measured alpha spectra, modern CAMs can also compensate for beta background to a large extent, while still maintaining good per formance capability A review o f background compensation methods is provided by Re ference [13] 28 © ISO 2017 – All rights reserved ISO 16639:2017(E) Annex C (informative) Normalized concentration and exposure In some countries, concentration measurements are normalized using the term derived air concentration (DAC) DAC is defined as the derived limit on the activity concentration in air o f a specified radionuclide, calculated such that reference individual, breathing air with constant contamination at the DAC while per forming light physical activity for a working year, would receive an intake corresponding to the annual limit on intake for the radionuclide in question ICRP and IAEA publish dose coe fficients for inhalation, such as those in Re ferences [6] or [9] These dose coe fficients, e inh , in Sv·Bq−1 , give committed effective dose per unit intake of each radionuclide in each chemical and physical form, that is, transportability Type (F = “ fast”; M = “moderate”; S = “slow”) EXAMPLE From the einh coe fficients and an occupational dose limit DL of 20 mSv⋅y−1 , the annual limit on intake (ALI in Bq) can be derived [see Formula (C.1)] ALI = NOTE DL e in h Using an annual occupational breathing rate and exposure time, the DAC (Bq·m−3 ) from ALI [see Formula (C.2)] DAC = where QBTE ALI Q B TE (C.1) can be derived (C.2) is typically taken as 400 m ; is the integrated exposure time, in h NOTE QB = 1,2 m3 ⋅h-1 and TE = 000 h (see Reference [9]) TE © ISO 2017 – All rights reserved 29 ISO 16639:2017(E) Annex D (informative) Example applications of evaluating sampling program sensitivity from the viewpoint of potential missed exposure NOTE These references come from Reference [5] NOTE Within this annex, read MDA (minimum detection activity) as the detection limit for activity and MDC (minimum detectable concentration) as the detection limit for activity divided by the associated volume, considering that volume uncertainty is negligible This annex provides sample applications of the PME concept in terms of Table In our examples we consider that ALI correspond to 000 DAC-h and also to 20 mSv·y-1 As a first example, let us assume there is continuous workplace sampling (see the first row o f Table ) per formed throughout the year, that air samples are obtained weekly, and that annual doses related to >40 DAC-h o f exposure should not be missed The recommended minimum detection limit of this particular retrospective air-sampling program should not exceed 0,02 (i.e 1/50) of the PME, or 0,8 DAC-h per sample As an additional example, let us assume there is some type o f temporary workplace operation (e.g cutting or welding as part o f a maintenance activity; see the second row o f Table 2), and that doses related to >40 DAC-h (a PME o f mSv per year) o f exposure should not be missed The minimum detection capability o f this particular air sampling during the job should not exceed 40 DAC-h (i.e the PME for this example) for the count o f the sample Now let us assume that this temporary workplace operation occurs four times per year, that air sampling is per formed for each operation, and that the annual PME remains at mSv The minimum detection capability o f this particular air sampling program should not exceed 40 ÷ 4, or 10 DAC-h per sample for each of the four samples For a final example, let us assume that continuous air monitoring (see the last row o f Table 2) is per formed throughout the year with an alarming CAM and that any acute dose related to >40 DAC-h o f exposure should not be missed (i.e failure to alarm) The recommended minimum detection capability of this particular continuous air-sampling program should not exceed 40 DAC-h This value should include contributions from both the CAM alarm set-point, as well as the CAM placement, since the latter can typically modi fy the former by orders-o f magnitude, i.e the so-called dilution factor[11] When the task o f the air sampling is to measure the concentration down to some specific MDC (e.g for purposes o f posting or respiratory protection), the MDC can be achieved through minimizing the MDA o f the assay system and/or maximizing (within practical limits) the sample flow rate, sampling time, and collection e fficiency When the task o f the air sampling is to measure a specific minimum detectable number o f DAC-h (e.g for the purposes other than posting or respiratory protection), then for example, in order to achieve a 10 DAC-h sensitivity for an exposure time o f eight hours, the MDC is 1,25 DAC (i.e 10 DAC-h ÷ h = 1,25 DAC) The DAC-h exposure can be estimated as shown in Formula (D.1) 30 © ISO 2017 – All rights reserved ISO 16639:2017(E) DAC-h = A where A Q B 000 q ALI (D.1) collected activity, in Bq; breathing rate of 1,2, in m3 ·h-1 ; q sampling flow rate, in m ·h−1 ; 000 (DAC-h) is exposure corresponding to ALI (Bq); ALI annual limit of intake, in Bq Formula (D.1) assumes the exposure time is equal to the sampling time As an example of this approach, i f the activity on the filter was 0,000 o f an ALI and the flow rate was 1,2 m ·h−1 , then the DAC-h exposure would be DAC-h QB © ISO 2017 – All rights reserved 31 ISO 16639:2017(E) Bibliography [1] ISO 17873, Nuclear facilities — Criteria for the design and operation of ventilation systems for [2] ISO 20553, Radiation protection — Monitoring of workers occupationally exposed to a risk of [3] ISO 26802, Nuclear facilities — Criteria for the design [4] ISO 2889, Sampling airborne radioactive materials from the stacks and ducts of nuclear facilities [5] ANSI/HPS N13.56:2012 Sampling and Monitoring Releases o f Airborne Radioactivity in the Workplace Health Physics Society, McLean, Virginia, USA [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] 32 nuclear installations other than nuclear reactors internal contamination with radioactive material ventilation systems for nuclear reactors and the operation o f containment and IAEA International Basic Safety Standards for Protection again st Ionizing Radiation and for the Safety of Radiation Sources Safety Series No.115 International Atomic Energy Agency, Vienna, 1996 ICRP Report on the Task Group on reference Man: Anatomical, Physiological and Metabolic Characteristics ICRP Publication 23 International Commission on Radiological Protection, 1975 ICRP Human Respiratory Tract Model for Radiological Protection ICRP Publication 66 Ann ICRP 1994, 24 (1-3) ICRP Age-Dependent Doses to Members of the Public from Intake of Radionuclides: Part Compilation o f Ingestion and Inhalation Dose Coe fficients ICRP Publication No 72 Ann ICRP 1996, 26 (1) ICRP The 2007 Recommendations of the International Commission on Radiological Protection ICRP Publication 103 Ann ICRP 2007, 37 (2-4) Jus tus A.L Derivation of continuous air monitor equations for DAC and DAC-h Health Phys 2010, 98 (5) pp 735–740 Porstend örf er J Properties and behaviour of Radon and Thoron and their decay products in the air J Aerosol Sci 1994, 25 (2) pp 219–263 Rodgers J.C The practice of continuous air monitoring for alpha-emitting radionuclides In: Radioactive air sampling methods, (M aiello M.L., & H oover M.D eds.) CRC Press, Boca Raton: 2011, pp 285–313 Whicker J.J., Rodgers J.C., Fairchild C.I., S cripsick R.C., L opez R.C Evaluation of continuous air monitor placement in a plutonium facility Health Phys 1997, 75 (5) pp 735–743 Whicker J.J., Rodgers J.C., M oxle y J.S A quantitative method for optimized placement of continuous air monitors Health Phys 2003, 85 (5) pp 599–609 Z hengyong L., & Whicker J.J Considerations for data processing by continuous air monitors based on accumulation sampling techniques, Health Phys 2008, 94 (suppl.1), pp S4–S15 Whicker J.J., & Jus tus A Probabilistic model evaluation of continuous air monitor response for meeting radiation protection goals, Health Phys 2009, 97 (3), pp 228–241 © ISO 2017 – All rights reserved ISO 16639:2017(E) ICS 13.280 Price based on 32 pages © ISO 2017 – All rights reserved